There is a need to polymerize olefins such as ethylene and propylene to satisfy the large market demand for various plastics. In the past, olefins have been polymerized by means of a catalyst containing chromium deposited onto a support which may be silica, alumina, zirconia or thoria. The synthesis of these catalysts in some cases comprises transferring the described support to a mixing tank to form an isopentane (iC5) slurry. Once the slurry is formed a titanium ester such as titanium isopropoxide, Ti(OPr)4, was added to the slurry. This process then requires drying the slurry to a free-flowing powder. In this dry form the mixture is then transferred to the fluid bed activator and activated in air at temperatures of 550° C. to 850° C. An analogous process is disclosed in U.S. Pat. No. 3,976,632 to Delap et al., and a similar process is disclosed in U.S. Pat. No. 3,996,163 to Crump et al. These methods are time consuming and costly. Accordingly, there is an incentive to investigate and bring to market cheaper and faster methods of catalyst preparation. Specifically, a need exists for a process that is simpler, faster and does not require the use of a titanium ester such as Ti(OPr)4. The claimed invention fills such a need by providing a simpler process for the production of titanated supports, as described herein.
According to C.E. Marsden in Plastics, Rubber and Composites Processing and Applications Vol. 21, No. 4, 193-200 (1994), the promotional effect of titanium on chromium catalysts for ethylene polymerization is to reduce polymer molecular weight (higher melt index) and broaden the molecular weight distribution. Additionally according to C.E. Marsden, the catalysts exhibit rapid start of polymerization (reduced induction time) and higher activity.
EP patent 0,314,385 assigned to Mobil Oil discloses the preparation of titanated chromium on silica catalysts useful for gas phase polymerization of ethylene. The combination of the catalyst is introduced with at least one organomagnesium compound, RMgR′, either prior to feeding or within the polymerization vessel. The catalyst may be titanated using a number of titanium halides, alkyl titanium halides, alkyl titanium alkoxides, alkoxy titanium halides or titanium alkoxides.
EP patent 0,882,740 assigned to FINA discloses the titanation of chromium based catalysts under specific conditions. Alkyl titanium alkoxides or titanium alkoxides are added to the chromium containing catalysts while at a temperature of at least 300° C. in a fluidized bed under nitrogen.
U.S. Pat. No. 3,780,011 assigned to Chemplex discloses the modification of chromium on SiO2 catalyst by the addition of a titanium ester to a bed of fluidized catalyst held at a temperature of at least 300° C. The esters have the general formula RnTi(OR1)m, wherein n+m=4.
U.S. Pat. No. 4,016,343 assigned to Chemplex discloses titanation of silica prior to the addition of the chromium compound to the titanated support. The chromium compound is a tetravalent alkoxide and the titanated support is prepared using titanium esters of the general formula RnTi(OR1)m, wherein n+m=4, TiX4, TiO2, alkanolaminetitanates, and titanium acetylacetonate compounds. Titanation is accomplished by mixing the support and the titanium compound and heating at a temperature of about 150-1200° C.
U.S. Pat. No. 4,184,979 assigned to Chemplex discloses the preparation of catalyst by dry blending Chromium(acac)3 with a silica support. The mixture is then heated to a temperature of 230-540° C. The catalyst is titanated by adding the liquid titanium compound to a fluidized bed of the chromium catalyst or by passing vapors of the titanium compound through the fluidized bed of the chromium catalyst.
U.S. Pat. No. 4,368,303 to McDaniel discloses a catalyst produced by forming a silica hydrogel; drying said hydrogel to form a xerogel; anhydrously incorporating a titanium compound into said xerogel; wherein chromium is introduced by either coprecipitating same with said silica hydrogel, by combining a water-soluble chromium compound with said hydrogel, or adding anhydrous solution with said hydrogel, or adding anhydrous solution of a chromium compound soluble in non-aqueous solvents to said xerogel; and after said drying and after said chromium is introduced, activating the resulting dried, chromium-containing composition by means of an activation procedure which comprises treatment at an elevated temperature in an atmosphere containing oxygen. In this manner, McDaniel does not disclose the use of a solid titanium compound.
U.S. Pat. No. 4,384,987 to Hawley discloses a method for preparing a polymerization catalyst comprising the steps of contacting a material comprising silica-supported chromium oxide or a compound oxidizable to chromium oxide with a solution of a permanganate compound; heating the thus-contacted material in a reducing atmosphere at a temperature in the range of about 600° C. to about 1100° C.; and then heating the material in an oxygen-containing atmosphere at a temperature in the range of about 450° C. to about 1000° C. for at least about one-half hour. In this manner, Hawley does not disclose the use of a solid titanium compound.
U.S. Pat. No. 4,402,864 assigned to Phillips Petroleum discloses the use of titanium polymers for titanation. The polymers are prepared from Ti(OR)4 and water. The soluble titanium polymer, e.g., TiO2(O-iC3H7)6 is most conveniently added to a hydrocarbon slurry of the support.
U.S. Pat. No. 4,728,703 assigned to BASF discloses the preparation of a chromium on silica catalyst by combining a slurry of silica in an alkane with finely divided CrO3, then adding alcohol, then adding Ti(OR)4, then the mixture is dried, and then the mixture is heated as a fluidized bed first in nitrogen and then in air.
A process for the preparation of activated catalyst for the polymerization of olefins in the absence of a solvent was disclosed in U.S. Pat. No. 5,573,993 to Koch. Koch discloses a three stage process, which includes a preactivation stage of heating a mixture of a powdered chromium salt with a support to a temperature below the melting temperature of the chromium salt for a period of between 0.5 hours and 18 hours, and then heating the mixture to an activation temperature. This method takes about 23 hours to complete. In this manner, Koch does not disclose a process which includes the reaction of a solid titanium compound.